title: Multichannel recording of tibial-nerve somatosensory evoked potentials.
abstract: OBJECTIVE
  The topography of the peaks of tibial-nerve somatosensory evoked potential (SEP) varies among healthy subjects, most likely because of differences in position and orientation of their cortical generator(s). Therefore, amplitude estimation with a standard one- or two-channel derivation is likely to be inaccurate and might partly cause the low sensitivity of SEP amplitude to pathological changes. In this study, we investigate whether 128-channel tibial-nerve SEP recordings can improve amplitude estimation and reduce the coefficient of variation.
  
  
  METHODS
  We recorded tibial-nerve SEPs using a 128-channel EEG system in 48 healthy subjects aged 20 to 70 years (47 provided analyzable data). We compared P39, N50, and P60 amplitudes obtained with a 128-channel analysis method (based on butterfly plots and spatial topographies) with those obtained using a one-channel conventional configuration and analysis. Scalp and earlobe references were compared.
  
  
  RESULTS
  Tibial-nerve SEP amplitudes obtained with the 128-channel method were significantly higher as compared to the one-channel conventional method. Consequently, the coefficient of variation was lower for the 128-channel method. In addition, in both methods, the N50-peak amplitude was sometimes hard to identify, because of its low amplitude. Besides, in some subjects, the N50 peak, as obtained with the conventional method, rather seemed to be a period between two positivities rather than an activation peak on itself.
  
  
  CONCLUSIONS
  The 128-channel method can measure tibial-nerve SEP amplitude more accurately and might therefore be more sensitive to pathological changes. Our results indicate that the N50 component is less useful for clinical practice.
authors.affiliation: Department of Neurology, University Medical Center Groningen, University of Groningen, PO Box 30.001, 9700 Groningen, The Netherlands. w.j.g.van.de.wassenberg@neuro.umcg.nl
authors.forename: W J G
authors.initials: WJ
authors.lastname: van de Wassenberg
authors.forename: W J
authors.initials: WJ
authors.lastname: Kruizinga
authors.forename: J H
authors.initials: JH
authors.lastname: van der Hoeven
authors.forename: K L
authors.initials: KL
authors.lastname: Leenders
authors.forename: N M
authors.initials: NM
authors.lastname: Maurits
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D000465:Algorithms; D003627:Data Interpretation, Statistical; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007206:Individuality; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013003:Somatosensory Cortex / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology*; D055815:Young Adult